Aqueous composition for outdoor paints, indoor paints, facade paints and roof paints

ABSTRACT

The present invention relates to an aqueous composition for outdoor, indoor, facade and roof paints having a biocidal action.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an aqueous composition for outdoor,indoor, facade and roof paints having a biocidal action.

2. Description of Related Art

Today, dispersion paints are used as a composition for outdoor, indoor,facade and roof paints, in particular in the construction industry. Whenused, in particular, in areas of high humidity, such as, for example, indamp rooms, for example in the food and textile industry, in swimmingbaths, kitchens, bathrooms and cellars, but also in living spaces,sleeping spaces and offices, and if organic components are present atthe same time, there is a danger of the formation of mould. There isalso an increased risk of mould fungus formation in areas of missing orinsufficient insulation of the external walls and/or of thermal bridgesor thermal weak spots in the external envelope. In practice, the areasof facades and roofs can often be found to be affected on the surfaceswith algae, lichens, as well as fungi. In the state of the art, biocidaladditives are used in compositions for indoor, facade and roof paints,the biocidal additives at the same time acting as film and potpreservatives, which, however, have the disadvantage of being toxic,which is why the use of these substances is subject to legal regulationsas regards to type and quantity. In addition, these substances have aperiod of action that is very limited with regard to its duration, dueto their volatility and their lack of chemical long-term stability.Thus, isothiazolinones are often used as preservatives in dispersionpaints. However, it is known that compounds such as5-chloro-2-methyl-2,3-dihydroisothiazole-3-one (MCI) and2-methyl-2,3-dihydroisothiazole-3-one (MI) have an allergenic potentialor are toxic.

BRIEF SUMMARY OF THE INVENTION

The inventors of the present invention therefore addressed the object ofproviding an aqueous composition for outdoor paints, indoor paints,facade paints and roof paints, in particular a dispersion paint having astrong biocidal action, and thus, an extremely low susceptibility withregard to the colonization by microorganisms. In addition, they foundthat the biocidally active ingredients did not discolour the paint, thatthey are compatible with the paint components, non-volatile, odourless,and, in particular, non-toxic and permanently effective.

Even though the biocidal action of silver has been known since mediaevaltimes, and though use is made of this action in certain applicationseven today, the possibility of the use of elementary silver in liquid,aqueous paint compositions for indoor, facade and roof paints is notmade obvious or even mentioned in any of the documents relating to theseapplications.

Some of the documents found in a search in this regard are listed below,which describe the applications of elementary silver as an antimicrobialor antifungal agent.

Thus, WO 03/080911 discloses a fibre-like material comprising anano-silver coating having nano-silver particles with diameters of lessthan 100 nm. The production of this fibre-like material is carried outby immersing degreased yarns in nano-silver solutions. From WO2004/059027, a method for depositing an antimicrobial surface ontosubstrates is known, wherein antimicrobial metals are applied ontosubstrates by plasma deposition. Anti-microbial powder coatingcompositions are known from US 2004/0180098, US 2003/0096017. FromEP-A-1433871, a method is known for providing anti-bacterial activity ona surface of a body using nanoparticular metals. Anti-microbial adhesiveand coating substances are known from WO 03/024494. These, however, arepurely organic compositions, which are not expected to have activity inaqueous compositions, and that, furthermore, would not comply withtoday's ecological requirements.

Thus, none of the above-mentioned documents discloses the application ofsilver or silver ions as biocidal agent in aqueous paint compositionsfor outdoor, indoor, facade and/or roof paints, in particular aqueousdispersion paints, or makes this application obvious.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a PCS analysis of a nano-Ag suspension (1% by vol in H₂O)according to the invention.

FIG. 2 shows a REM (reflecting electron microscope) image of the sampleproduced in the exemplary embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors surprisingly found that silver displays a biocidalaction under the special conditions of aqueous paint compositions foroutdoor, indoor, facade and/or roof paints. The inventors further foundthat a particularly pronounced biocidal action is achieved if theaqueous paint composition according to the invention contains silver ina nanoparticular form. An even more pronounced biocidal action can beachieved if silver in the form of a soluble silver salt, such as, inparticular, silver nitrate, is added to the aqueous paint composition,apart from nanoparticular elementary silver. For a given binding agentsystem, the bioavailability of the silver ions, and thus, the biocidalaction of the paint agent, can here be adjusted in a customized manneras a function of time, via the proportion of elementary silver tosoluble silver salt. Particularly surprisingly, the present inventorsfound that a synergetic increase of the biocidal action is achieved bythe addition of chitosan to the paint composition according to theinvention. A further improvement can be achieved by the additional useof nanoparticular ZnO (zinc oxide). Preferably, the nanoparticular zincoxide has a mean grain size of less than 500 nm, more preferably of lessthan 100 nm, still more preferably of less than 50 nm. The particle sizerange of between 5 to 50 nm is particularly active. The particle size isdetermined by photon correlation spectroscopy. If the compositioncontains nanoparticular zinc oxide, it is expediently present in anamount of 0.000001 to 25% by mass, relative to the total mass of thecomposition.

Thus, the inventors were successful in providing an aqueous paintcomposition that is highly compatible with regard to ecology and health,which contains non-volatile anti-microbial agents and therefore exhibitsno allergenic or toxic actions.

Therefore, the subject matter of the present invention are aqueouscompositions for indoor, outdoor, facade and/or roof paints containingsilver. Aqueous compositions for outdoor, indoor, facade and roof paintswithin the sense of the invention are water-based coating agents, inparticular aqueous plastic dispersion paints containing at least, inparticular, one water-dispersible organic and/or inorganic binding agentdispersed therein. They are preferably used when interior spaces, facadeand roof surfaces are being painted the first time or repainted. Theirapplication is carried out, in particular, by rolling or brushing, alsoby spraying in the case of systems with low viscosity. In any case, thecomposition according to the invention is liquid or brushable at roomtemperature (20° C.).

The paint composition according to the invention contains silver.Particularly preferably, the paint composition according to theinvention contains silver in nanoparticular form, that is, the particlesof the elementary silver have a mean particle size (diameter) of lessthan 500 nm, more preferably of less than 100 nm, still more preferablyof less than 50 nm. A mean particle size of 5 to 50 nm is particularlyactive. The particle size here is determined by photon correlationspectroscopy.

Due to the use of the nanoparticular silver in the compositionsaccording to the invention, an unexpectedly high biocidal action isachieved in a sustained manner, relative to the silver content, so thatthe quantity of the silver used can remain small.

In contrast to the organic biocidal active substances hitherto used inpaint systems, the nanoparticular silver used in accordance with theinvention has a high chemical long-term stability. Since paints oftenremain applied over many years, and as outdoor paints, especially, areexposed to strong meteorological influences, such as rain andinsolation, the use according to the invention of the stablenanoparticular silver constitutes a substantial improvement in providingbiocidally equipped aqueous paint systems, in particular with regard tothe long-term action.

Mechanistically seen, a thin, not completely closed oxide layer havingAg₂O as a main component forms on the nanosilver particles. Solvolysisleads to the formation of Ag⁺ cations, which, as the actual activecomponent, block the thio enzymes of the microorganisms.

The content in the paint composition according to the invention ofelementary, in particular nanoparticular silver, preferably is less thanabout 500 ppm, preferably less than about 100 ppm. Particularlypreferably, the nanoparticular silver is present in an amount of 1 to100 ppm, more preferably of 1 to 10 ppm, relative to the total mass ofthe paint composition.

Furthermore, the inventors surprisingly found that the addition ofsilver ions by adding preferably soluble silver salts, such as, inparticular silver nitrate, combined with the nanoparticular silvercauses a synergetic effect with regard to the biocidal action relativeto the total quantity of the silver used.

As was already mentioned, it is furthermore possible to adjust in acustomized manner the bioavailability of the silver ions as a functionof time by adjusting the proportion of nanoparticular silver to solublesilver salt for a given binding agent.

The quantity of the soluble silver salt used, relative to the total massof the paint composition, preferably is less than about 500 ppm,preferably less than about 100 ppm. Particularly preferably, thequantity of the silver salt silver is 1 to 100 ppm, more preferably 1 to10 ppm, relative to the total mass of the paint composition.

Furthermore, the present inventors were successful, surprisingly, inincreasing the biocidal action of the paint composition according to theinvention in a synergetic manner by adding chitosan (trade name for thedeacylated chitin (CAS 9012-6-4. C.—see Fiedler, Lexikon derHilfsstoffe, Editio Cantor Verlag, 5th edition, 2002)) and/or a chitosanderivative, so that there is the possibility of further reducing thequantity of silver used. Chitosan that can be used in the invention has,for example, a molecular weight of 3,000 to 700,000, and is commerciallyavailable (see, for example, EP-A-0 377 091). The synergistic mode ofaction of the chitosan in cooperation with the silver used is based onthe biocidal growth taking place in accordance with differentmechanisms, with biochemical processes also being of significance inbuilding up the cell walls of the bacteria or fungi. Chitosan interfereswith the metabolism for building up the chitin cell walls and thusinhibits cell growth. It was surprising that chitosan had this actionalso under the special chemical conditions of aqueous paint systems.

The use of the combination of active substances of silver, in particularnanoparticular silver, in particular combined with silver salts, andchitosan furthermore makes an additional degree of freedom available forthe adjustment of the bioavailability and leaching rate of the silver asa function of the concrete requirement profile and the concrete paintsystem. According to the invention, chitosan, in case of its use, ispreferably used in an amount of about 0.1 to 10% by mass, preferably ofless than about 5 percent by mass, still more preferred less than 1% bymass, in each case relative to the total mass of the composition. Theminimum quantity used of the chitosan, in case of its use, is at leastabout 0.1% by mass (mass percent), in each case relative to the totalmass of the composition.

According to the invention, the use of chitosan derivatives is alsopossible, e.g. N,O-carboxymethyl chitosan, chitosan hydrochloride,chitosan acetate and chitosan lactate. In addition to the biocidalaction, the absorber action due to the secondary or tertiary structureof the molecular chain must be emphasized. One or more chitosanderivatives can be used in combination. Furthermore, one or morechitosan derivatives can be used also in combination with chitosan.Since the chitosan derivatives, both amongst themselves as well ascompared to chitosan, differ in particular with regard to theirsolubility in water, further possibilities of specifically adjusting thebioavailability, and thus, the biocidal action (biocidal action spectrumand action period).

The paint composition according to the invention preferably contains atleast one, in particular water dispersible, binding agent, in particularat least one inorganic and/or organic binding agent.

Organic binding agents are, for example, selected from the groupconsisting of vinyl-containing, such as styrene-containing,acrylate-containing and vinyl acetate-containing, urethane-containing,ester-containing, polymers or copolymers thereof, silicone resins andepoxy resins. Preferred organic binding agents are acrylic resins. Inorder to be water-dispersible, they generally have in particular ionicgroups, such as, for example, ammonium chloride. According to theinvention, one or more binding agents can be used in combination witheach other.

The organic binding agents are expediently contained in the compositionsaccording to the invention in quantities of up to 60% by mass. Theminimum quantity of the organic binding agents expediently is about 5%by mass, relative to the total quantity of the composition. Preferably,the compositions according to the invention contain about 10 to 40% bymass of the organic binding agent.

The inorganic binding agents are, for example, selected from lime, whitecement and potassium water glass, the latter being preferred. Lime isused, for example, in the form of calcium hydroxide, as pit lime etc,white cement is used in powder form, and potassium water glass as anaqueous solution of potassium silicate (fixative) as binding agent forso-called silicate paints. The quantity of the inorganic binding agentexpediently is maximally about 30% by mass, expediently at least about1% by mass, relative to the total quantity of the composition.

Inorganic and organic binding agents can also be used in combination.Organic binding agents are preferably used without inorganic bindingagents. Inorganic binding agents are preferably used in combination withorganic binding agents.

The composition according to the invention is an aqueous composition. Ittherefore preferably contains at least 10, more preferably at least 20,still more preferably at least 30% by mass of water. It can additionallyalso contain organic solvents. The quantity of the organic solvent,however, preferably is less than about 20% by mass, more preferably lessthan 10% by mass, still more preferably less than about 5% by mass.

The composition according to the invention preferably is a so-calledplastic dispersion paint, which, according to DIN EN 971-1: 1996-09, isa coating substance in which an organic binding agent dispersed in wateris present. With regard to their degree of gloss, they are availablefrom matte to glossy, and are particularly used when interior spaces,facade and roof surfaces are being painted the first time or repainted,the application preferably being carried out by rolling or brushing.

Furthermore, the paint compositions according to the inventionexpediently contain about up to 50% by mass colouring agents, such aspigments and dyes. Examples for pigments are titanium dioxide, ironoxide, magnesium oxide, zinc chromate, carbon black, barium sulphate.Dyes include, for example, para red, thioindigo, antrachinon,phthalocyanine blue and azo dyes.

In addition, typical inorganic or organic filler, such as carbonates,e.g., calcium carbonate; sulphates, e.g. calcium sulphate; silicates,e.g. talc, quartz; silicic acid, e.g. glass spheres, glass fibres;hollow microspheres; organic fillers, e.g. organic hollow microspheres,polymer fibres, cellulose fibres, can be used.

In addition, typical additives can be used, such as processing aids,such as dispersion aids, thickening agents, defoamer, stabilizers,cross-linking agents, etc.

The compositions according to the invention are capable, in particular,of inhibiting, controlling or eliminating the growth of bacteria, fungi,but also, surprisingly, the growth of algae, mosses and lichens,depending on the concentration of the biocidally active components. Theactivity against lichens and mosses is particularly useful in the caseof roof paints because, as is known, roofs can already be overgrownafter a few years which leads to considerable adverse effects withregards to aesthetic appearance, but also with respect to function.

In particular the composition according to the invention is capable ofinhibiting or stopping the growth of bacteria, such as Gram-positivebacteria and Gram-negative bacteria, such as, for example, of Chlamydiatrachomatis, Citrobacter, Providencia stuartii, Vibrio vulnificus,Staphylococcus aureas, Staphyloccus epidermidus, Escheria coli,Pseudomonas maltophilia, Serratia marcesens, Bacillus subtilis, Bacilluscloacae, Bacillus allantoides, Bacillus foecalis alkaligenes,Pneumobacillus, nitrate-negative Bacillus, Streptococcus facades,Streptococcus hemolyticus B, Salmonella typhinurium, Salmonellaparatyphi C, Salmonella morgani, Pseudomonas aeruginosa. Furthermore,the composition according to the invention is also capable of inhibitingthe growth of certain higher organisms, such as algae, fungi(Aspergillus, in particular Aspergillus niger, Aureobasidium, Botrytis,Candida albicans, Ceratostomella, Chaetomium, Cuvularla, Fusarlum,Gliocladium virens and Penicillium species), yeasts and spores.

The production of the aqueous composition according to the invention iscarried out, in particular, by producing a commonly used plasticdispersion paint to which the nanoparticular silver is added in the formof a suspension. Nanoparticular silver suspensions are known from theprior art and can be obtained commercially. FIG. 1, for example, showsthe result of a PCS analysis of a nano-Ag suspension (1% by vol in H₂O)that is applicable according to the invention.

In a preferred embodiment, silver nitrate is added to the paintcompositions according to the invention simultaneously. In anotherpreferred embodiment, chitosan or chitosan derivatives are added in thequantities specified above.

In practical application, the combination of the biocidal activesubstances is provided in the form of an aqueous suspension forincorporation into a paint.

The aqueous paint compositions according to the invention can be used,in particular, in damp areas, such as swimming baths etc. In particular,application takes place in damp spaces in which the formation of mouldis to be suppressed, such as, for example, in hospital areas, or inareas for foodstuff production, where biocidal surfaces are required,that is, generally in areas in which special hygienic requirements mustbe made.

The aqueous paint composition according to the invention can, inparticular, be applied onto existing paints, wallpaper, old and newplasters, plasterboards, etc., as an indoor paint composition.

The aqueous paint composition according to the invention can, inparticular, be applied onto existing paints, old and new plasters, sandylimestone, brickwork, boards of fibrated cement, metal such ascorrugated sheet metal, etc., as an outdoor paint composition.

The aqueous paint composition according to the invention can, inparticular, be applied onto concrete roofing tiles, corrugated metal,clay bricks, (artificial) slates, roofing tiles and panels containingfibrated cement, etc., as a roof paint composition.

The invention is explained in more detail by means of the followingexemplary embodiment.

The following mixture was prepared:

100 ppm nanoparticular silver having the grain size distribution shownin FIG. 1, 100 ppm silver nitrate (relative to the quantity of silver)and 1% by mass of chitosan were added to a commercial aqueous dispersionpaint (BIO00101 by the company Bioni-Shield, Oberhausen) and was workedin homogeneously (depending on a lesser degree of danger with regard tomicrobial contaminations, smaller contents of the biocidally activeadditives can be used).

FIG. 2 shows a REM image of the produced sample. Particles with a grainsize of about 200 nm, which are interpreted as pigments, can berecognized. Particles <15 nm that occur sporadically due to the lowconcentration are interpreted as nanoparticular silver.

Using the above produced paint, its biocidal activity was demonstratedin a suspension test following the preconditions given by Pharm. EU.,1997, supplement 2001, 2.6 “Methods of Biology”, 2.6.1 “Sterility test”,SOP Suitability test for nutrient media in accordance with the method ofdirect coating. The microorganism used was the fungus Aspergillus niger.

The direct smears with an inoculating loop according to the abovedescribed method showed no fungal growth at all for the paintcomposition according to the invention.

1. An aqueous paint composition comprising (a) elementary silver, (b)one selected from the group consisting of chitosan, chitosanderivatives, and combinations thereof (c) wherein the total weight ofchitosan and chitosan derivatives constitutes 0.1 to 10% by mass of theaqueous paint composition.
 2. The paint composition of claim 1, whereinthe silver is present in the form of particles.
 3. The paint compositionof claim 1, wherein the silver is present in the form of particleshaving an average particle size of less than 500 nm.
 4. The paintcomposition of claim 1, wherein the concentration of the elementarysilver is no greater than 500 ppm.
 5. The paint composition of claim 1,comprising chitosan derivatives, wherein the chitosan derivatives areselected from the group consisting of N,O-carboxymethyl chitosan,chitosan hydrochloride, chitosan acetate and chitosan lactate.
 6. Thepaint composition of claim 1, further comprising ZnO having a meanparticle size of less than 500 nm.
 7. The paint composition of claim 1,comprising at least one binding agent.
 8. The paint composition of claim7, wherein the binding agent is organic or inorganic.
 9. The paintcomposition of claim 8, wherein the at least one organic or inorganicbinding agent is water-dispersible.
 10. The paint composition of claim9, wherein the binding agent is an organic binding agent including amonomer selected from the group consisting of vinyl, styrene, acrylate,vinyl acetate, urethane, ester, polymers of the foregoing, copolymers ofthe foregoing, silicone resins, and epoxy resins.
 11. A method forcoating surfaces of building interiors, building exteriors, buildingfacades and roofs, comprising applying to a surface thereof the aqueouscomposition of claim
 1. 12. An aqueous paint composition comprising: (a)elementary silver, (b) silver salt and (c) one selected from the groupconsisting of chitosan, chitosan derivatives, and combinations thereof.13. The paint composition of claim 12, further comprising ZnO having amean particle size of less than 500 nm.
 14. The paint composition ofclaim 12, further comprising at least one binding agent.
 15. A methodfor coating surfaces of building interiors, building exteriors, buildingfacades and roofs, comprising applying to a surface thereof the aqueouscomposition of claim
 12. 16. A method of painting a surface comprisingapplying to the surface an aqueous composition including nanoparticulatesilver and at least one selected from the group consisting of chitosan,chitosan derivatives, nanoparticulate ZnO, and combinations thereof,wherein the aqueous composition comprises one selected from the groupconsisting of a biocide and a binding agent.
 17. A method for coatingsurfaces of building interiors, building exteriors, building facades androofs, comprising applying to a surface thereof the aqueous compositionof claim
 16. 18. A method of painting a surface comprising applying tothe surface an aqueous composition including nanoparticulate silver andat least one selected from the group consisting of chitosan, chitosanderivatives, nanoparticulate ZnO, and combinations thereof, wherein theaqueous composition further comprises a binding agent and a dispersingagent.
 19. A method for coating surfaces of building interiors, buildingexteriors, building facades and roofs, comprising applying to a surfacethereof the aqueous composition of claim 18.